1. Field of the Invention
This invention relates generally to roller mills, and more particularly to an improved roller mill drive. More specifically, the invention relates to an improved drive for a "double roller mill" having two pairs of parallel rolls in which the rolls in each pair are driven in opposite directions and at different speeds. The rolls driven at the higher speed are referred to as "fast" rolls, and the rolls driven at the lower speed are referred to as "slow" rolls.
2. Description of the Prior Art
A roller mill is used to reduce the particle size of a substance by grinding it between two steel rolls. In flour mills, wheat is fed to a roller mill which grinds the material to produce flour.
Probably most flour mills in this country today use a double roller mill for making flour. Each double roller mill, which is also referred to as a "roll stand", is commonly powered by a belt drive system that has been used in flour mills since approximately the early 19th century. This belt drive system is used on roller mills manufactured by Nordyke and Marmon Co., for example; and a similar belt drive system is shown in U.S. Pat. No. 2,549,501 to McClelland. This prior belt drive system includes two large flat belts. One belt turns the two fast rolls in one direction, while the other belt turns the two slow rolls in the opposite direction.
This belt drive includes separate pulleys on the fast rolls, and an idler pulley on a jackshaft, or tunnel shaft, that runs through the base of the roll stand. The drive belt for the fast rolls engages one fast roll pulley, the idler pulley on the jackshaft, and the other fast roll pulley, in that order. The fast roll drive belt is driven by a large drive motor on a lower floor of the flour mill below the roll stand. The drive motor powers a large drive pulley on a lineshaft that runs through the lower floor of the mill. The fast roll drive belt is engaged with the drive pulley on the lineshaft and then runs upwardly to the next floor of the mill where it engages the two fast roll pulleys and the idler pulley on the jackshaft. A second belt drive at the opposite end of the roll stand powers the two slow rolls. The second belt engages separate large pulleys on the slow rolls and a pulley on the jackshaft for transferring power from the fast roll drive, at one end of the roll stand, to the slow roll drive at the other end of the roll stand.
Flour mills continue to use this type of roller mill today, in part, because of the tremendous capital cost involved in replacing it with new roller mills. For example, a typical flour mill has a large number of these roll stands arranged in rows on one floor of the flour mill, while the drive motor and the lineshaft for each row are installed in the next floor below each row of roll stands. The roll stands in each row receive power from separate drive belts engaged with corresponding drive pulleys on the lineshaft. The drive belts all extend from the lineshaft in the lower floor to the roll stands on the next floor. A jackshaft tunnels through each machine, and separate belts for the fast and slow roll drives of each roll stand are engaged with the jackshaft.
Such an arrangement of roll stands requires extensive guarding around the drive motor, the lineshaft, and the various drive belts in the lower floor of the mill, and around the drive belts on opposite ends of each roll stand on the next floor. The guarding is required for safety to protect workers from the working parts of the machines.
Because of such guarding, it is a costly and timeconsuming job to frequently clean the flour dust that constantly collects inside the guarded regions of the mill. Frequent cleaning is required by various health ordinances to maintain sanitary conditions in the flour mill. The guarding must be removed to gain access for cleaning, and the entire row of roll stands must be shut down during cleaning.
In addition to the large initial cost and maintenance costs required by the prior belt-driven roller mill, there are also other problems, such as belt slippage and buildup of static electricity, which are inherent in using large flat belt drives. Moreover, the roller mill drive must be capable of delivering a large amount of power to drive both pairs of rolls. To provide large power-handling capability requires wide belts with large diameter pulleys which, in turn, occupy a large amount of space in the mill.
This invention provides an improved roller mill drive that avoids many of the disadvantages of the prior beltdriven roller mill drive described above.